Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F8/00—Chemical modification by after-treatment
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F8/00—Chemical modification by after-treatment
  • C08F8/30—Introducing nitrogen atoms or nitrogen-containing groups

Definitions

• the present invention relates to a nitrile group-containing fluoroelastomer having nitrile group in a molecular chain, particularly at the end of the molecular chain and a process for preparation thereof.
• the elastomer can give a crosslinked product having a very good sealing property, mechanical strength and ultra high heat resistance of not less than 300°C.
• Fluoroelastomers comprising a fluoromonomer unit as a recurring unit such as tetrafluoroethylene (TFE) are used widely as a sealing material to be used under strict environment since they exhibit excellent chemical resistance, solvent resistance and heat resistance. Particularly in the fields of aviation and space industries, semi-conductor production apparatuses and chemical plants, which are major applications of the fluoroelastomers, heat resistance of sealing at 300°C or more is demanded.
• TFE tetrafluoroethylene
• Such a crosslinked product having excellent heat resistance is obtained by firstly preparing a nitrile group-containing fluoroelastomer having nitrile group in a molecular chain as a cure site by copolymerizing perfluoro(vinyl ether) (CNVE) having nitrile group with TFE and perfluoro(alkyl vinyl ether) (PAVE) and then crosslinking the fluoroelastomer by triazine crosslinking with organotin, oxazole crosslinking with a bisaminophenol compound or tetraamine compound or imidazole crosslinking, as described, for example, in JP-A-58-152041 and JP-A-59-109546.
• CNVE perfluoro(vinyl ether)
• PAVE perfluoro(alkyl vinyl ether)
• CNVE for introducing nitrile group as a cure site requires a long synthesis step and is very expensive, and also the nitrile group in the obtained nitrile group-containing fluoroelastomer is unstable. Further a mechanical strength and sealing property at high temperature (compression set) of the obtained crosslinked product are insufficient.
• the inventors of the present invention have made various studies with respect to conventional nitrile group-containing fluoroelastomers and assumed that a reason why sufficient properties were not obtained was the fact that nitrile cure site group is present only as a pendant of a molecular chain. Thus the inventors have studied introduction of nitrile group into an end of the molecular chain. However in a conventional method described in Polymer Journal, Vol. 17, No.
• An object of the present invention is to provide a solid fluoroelastomer having, at the end, nitrile group functioning as a cure site, and an economical preparation process thereof.
• Another object of the present invention is to provide a novel synthesis process for converting amide group into nitrile group, and a dehydrating agent to be used therefor.
• the present invention relates to a process for preparing a nitrile group-containing fluoroelastomer by converting amide group contained in a polymer molecular chain of a solid fluoroelastomer into nitrile group in the presence of a dehydrating agent.
• the dehydrating agent to be used is in the form of gas or liquid. Particularly COF 2 is preferable.
• the solid nitrile group-containing fluoroelastomer to be prepared in the present invention which has nitrile groups at both ends and is represented by the formula (I): NC - (R f ) - CN wherein R f is a divalent fluoroelastomer chain, is a novel fluoroelastomer.
• the fluoroelastomer chain R f is a perfluoroelastomer chain of copolymer or terpolymer represented by the formula (1): wherein m/(n + p) is 95 to 50/5 to 50, n/p is 0/100 to 100/0, m + n + p is from 100 to 10,000, R f 1 is a perfluoroalkyl group having 1 to 8 carbon atoms, R f 2 is - (CF 2 CFYO) q R f 3 , in which R f 3 is a perfluoroalkyl group having 1 to 6 carbon atoms, Y is fluorine atom or a trifluoromethyl group, q is an integer of 1 to 5, or a perfluoroelastomer chain of terpolymer or tetrapolymer represented by the formula (2): wherein 1/m/(n + p) is 95 to 35/0 to 30/5 to 35, n/p is
• the fluoroelastomer composition particularly comprising a solid nitrile group-containing fluoroelastomer having nitrile groups at ends in the number of more than 1/2 of a total number of end groups of molecular chains of the fluoroelastomer provides a crosslinked product having excellent properties.
• the present invention relates to the process for preparing an amide group-containing fluoroelastomer which is a starting substance for the above-mentioned reaction for converting into nitrile group, by reacting a solid fluoroelastomer having ester group in a molecular chain thereof, particularly at the end of the molecular chain with ammonia or aqueous ammonia.
• the present invention relates to a solid amide group-containing fluoroelastomer having amide groups at both ends and represented by the formula (II): H 2 NOC - (R f ) - CONH 2 wherein R f is a divalent fluoroelastomer chain.
• the present invention relates to a novel process for synthesis of a nitrile compound which is represented by the formula (IV): R - CN wherein R is a monovalent organic group, and is prepared by dehydrating an amide compound represented by the formula (III): R - CONH 2 wherein R is as defined above, in the presence of COF 2 . It is advantageous to use COF 2 as the dehydrating agent for such a reaction for converting into nitrile group, from the viewpoint of yield, low boiling point and easy removal of un-reacted gas after the reaction.
• the present invention relates to the process for preparing a nitrile group-containing fluoroelastomer by converting amide group contained in a polymer molecular chain of a solid fluoroelastomer into nitrile group in the presence of a dehydrating agent.
• a fluoropolymer which is a starting material in the process for preparing the nitrile group-containing fluoroelastomer of the present invention is firstly (1) in the form of solid.
• a liquid fluorooil which is described in the above-mentioned Polymer Journal, has a relatively low molecular weight (10,000 or less) and comprises essentially a fluoroether unit, is excluded.
• conventional dehydrating agents can be used, but in case of a solid fluoropolymer, non-uniform reaction arises and a desired object cannot be obtained.
• the fluoropolymer has amide group in a molecular chain thereof.
• the amide group may be present in the molecular chain as a pendant or may be present as end group of the molecular chain. It is a matter of course that the amide groups may be present in the both forms.
• the present invention has an important meaning that it becomes possible to introduce nitrile group as end group, which has been so far impossible.
• the solid fluoroelastomer having nitrile groups at both ends which can be prepared by the process of the present invention and is represented by the above-mentioned formula (I) is a novel fluoroelastomer.
• an elastomer chain (R f in the formula (I)) on a trunk chain portion of the fluoroelastomer does not change substantially.
• the fluoroelastomer chain R f are, for instance, a perfluoroelastomer chain of copolymer or terpolymer represented by the formula (1): wherein m/(n + p) is 95 to 50/5 to 50, n/p is 0/100 to 100/0, m + n + p is from 100 to 10,000, R f 1 is a perfluoroalkyl group having 1 to 8 carbon atoms, R f 2 is - (CF 2 CFYO) q R f 3 , in which R f 3 is a perfluoroalkyl group having 1 to 6 carbon atoms, Y is fluorine atom or a trifluoromethyl group, q is an integer of 1 to 5, a perfluoroelastomer chain of terpolymer or
• conversion into nitrile group may be carried out after fluorination of the non-perfluoroelastomer chain with a fluorine gas or the like.
• the dehydrating agent is in the form of gas or liquid because the elastomer is in the form of solid.
• the dehydrating agent in the form of gas are, for instance, COF 2 , COCl 2 , SO 3 , and the like. Particularly COF 2 is preferable from the viewpoint of good yield, relatively moderate reaction conditions and easy treatment.
• Use of COF 2 as a dehydrating agent for converting amide group into nitrile group, i.e. nitrilation of amide group has novelty.
• Examples of the dehydrating agent in the form of liquid are, for instance, acetic anhydride, trifluoroacetic anhydride, ClCO 2 C 2 H 5 , and the like. Particularly trifluoroacetic anhydride is preferable from the viewpoint of a yield.
• an acid acceptor such as pyridine, triethylamine, or the like may be used together with those dehydrating agents.
• the reaction for converting amide group into nitrile group advances at a temperature of -20°C to 200°C. It is preferable to carry out the reaction under heating, particularly at a temperature of 50°C to 150°C from the viewpoint of a good yield and a short reaction time.
• the reaction pressure is from atmospheric pressure to 5 MPaG, preferably 1 to 2 MPaG.
• the reaction time is usually from about 10 hours to about 90 hours.
• the reaction can be carried out in the presence or absence of a solvent.
• a fluorine-containing solvent for example, FLORINATE (registered trademark) series available from SUMITOMO 3M LIMITED
• a fluorine-containing solvent for example, FLORINATE (registered trademark) series available from SUMITOMO 3M LIMITED
• the present invention relates to the process for preparing the amide group-containing fluoroelastomer which is a starting material for preparing the nitrile group-containing fluoroelastomer.
• the solid fluoroelastomer is usually prepared by radical polymerization of a fluorine-containing monomer by using a radical polymerization initiator.
• a radical polymerization initiator There are various compounds known as a radical polymerization initiator.
• a lot of general-purpose initiators, for example, ammonium persulfate, potassium persulfate, and the like are converted to carboxyl groups by acid treatment to be carried out when collecting a produced elastomer, thereby giving a fluoroelastomer having carboxyl groups at ends.
• a usual method which can be considered for converting the end carboxyl groups into amide groups suitable for nitrilation of the present invention is a method of firstly forming the carboxyl group into an ammonium salt with ammonia and then heating for dehydration.
• the present invention relates to the method of converting ester group into amide group by reacting a solid fluoroelastomer having ester group in a molecular chain, particularly at the end of the molecular chain with ammonia or aqueous ammonia.
• reaction conditions which can be used are mentioned below.
• the esterification of the carboxyl group-containing fluoroelastomer can be carried out under usual esterification conditions, for example, by a method of reacting the elastomer with an alcohol in the presence of an acid catalyst, a method of converting into an acid chloride with thionyl chloride and then reacting with an alcohol, or the like method.
• Examples of the alcohol to be used for the esterification are, for instance, methanol, ethanol, 1-propanol, 2-propanol, and the like. Particularly methanol is preferable from the viewpoint of excellent yield and economy.
• nitrile group is introduced as a pendant of a fluoroelastomer.
• a nitrile group-containing fluoromonomer to be used for the introduction of nitrile group is very expensive, and as a result, the obtained nitrile group-containing fluoropolymer is expensive.
• nitrile group can be introduced as a pendant by copolymerizing an inexpensive carboxyl group-containing fluoromonomer to introduce carboxyl group as a pendant, and after carrying out esterification of the carboxyl group as mentioned above to form into amide group, converting into nitrile group.
• the perfluoroelastomer can be prepared from the non-perfluoroelastomer by fluorinating the non-perfluoromonomer with a fluorine gas, or the like and then carrying out the nitrilation because if the non-perfluoromonomer is fluorinated after the nitrilation, nitrile group is fluorinated.
• the method of converting amide group into nitrile group in the presence of COF 2 which is a dehydrating agent is a novel method.
• This reaction is not a reaction inherent to the amide group-containing fluoroelastomer and can be applied to the nitrilation reaction of general amide compounds including low molecular weight compounds.
• the present invention further relates to the process for synthesis of the nitrile compound represented by the formula (IV): R - CN wherein R is a monovalent organic group, by dehydrating the amide compound represented by the formula (III): R - CONH 2 wherein R is as defined above, in the presence of COF 2 .
• Examples of the monovalent organic group represented by R are various organic groups such as fluoroelastomer chains having a residue of polymerization initiator or chain transfer agent or a group derived therefrom at one end thereof, a linear or branched hydrocarbon group which has 1 to 20 carbon atoms and may be substituted by one or more halogen atoms, CF 3 CONH 2 , CH 3 CONH 2 , C 2 F 5 CONH 2 , C 2 H 5 CONH 2 , C 6 H 11 CONH 2 , C 6 H 5 CONH 2 and C 7 H 15 CONH 2 .
• the process can be applied to a liquid fluorooil mainly comprising a fluoroether unit which is described in the above-mentioned Polymer Journal.
• reaction conditions for the synthesis may be the same as in the above-mentioned nitrilation reaction of the solid fluoroelastomer.
• a principal object of introducing nitrile group is, as mentioned above, to use the nitrile group as a cure site of the solid fluoroelastomer. Particularly by introducing nitrile group into at least one end group, preferably into the both end groups, mechanical properties, heat resistance and compression set of a crosslinked product can be enhanced.
• the number of nitrile groups may be more than 1/2 of the total number of end groups of the obtained fluoroelastomer, preferably 70 % or more, particularly preferably 90 % or more.
• the fluoroelastomer may contain at least one fluoroelastomer chain having nitrile groups at its both ends. It is preferable that the remaining cure sites may be carboxyl group, ester group or amide group.
• the present invention further relates to the fluoroelastomer composition comprising the above-mentioned nitrile group-containing fluoroelastomer. It is preferable that a crosslinking agent is contained in the composition.
• the nitrile group-containing fluoroelastomer of the present invention can be crosslinked by triazine crosslinking, oxazole crosslinking, thiazole crosslinking, imidazole crosslinking, and the like. Particularly oxazole crosslinking is preferable from the viewpoint of good compression set, heat resistance and economy.
• crosslinking agent examples include organotin compounds such as tetraphenyltin and triphenyltin hydride for the triazine crosslinking; bisaminophenols such as bisaminophenol AF for the oxazole crosslinking; bisaminothiophenols such as bisaminothiophenol for the thiazole crosslinking; tetraamines such as bis(1,2-phenylenediamine) and 2,2-bis(3,4-diaminophenyl)hexafluoropropane for the imidazole crosslinking; and the like.
• organotin compounds such as tetraphenyltin and triphenyltin hydride for the triazine crosslinking
• bisaminophenols such as bisaminophenol AF for the oxazole crosslinking
• bisaminothiophenols such as bisaminothiophenol for the thiazole crosslinking
• tetraamines
• Crosslinked products obtained from the fluoroelastomer of the present invention are excellent in heat resistance, chemical resistance, physical properties in normal state, compression set, plasma resistance, cleanliness, and the like, and can exhibit very excellent characteristics as various materials for sealing members, gaskets, hoses and rolls.
• a 6,000-ml stainless steel autoclave having no ignition source was charged with 2,340 ml of pure water, 23.4 g of : as an emulsifying agent and 0.21 g of disodium hydrogen phosphate ⁇ 12H 2 O as a pH control agent, and after replacing the inside of the system with nitrogen gas sufficiently for deaeration, the autoclave was heated up to 50°C with stirring at 600 rpm. Then perfluoro(methyl vinyl ether) (PMVE) was introduced so that the inside pressure became 0.3 MPaG (3.0 kgf/cm 2 G) in a gauge pressure and further tetrafluoroethylene (TFE) was introduced until the inside pressure became 0.4 MPaG (4.1 kgf/cm 2 G). Then 12.3 g of ammonium persulfate (APS) dissolved in 30 ml of water was introduced with a pressurized nitrogen gas to initiate a reaction.
• PMVE perfluoro(methyl vinyl ether)
• TFE tetrafluoroethylene
• 1,800 Grams of the obtained aqueous dispersion was diluted with 5,400 g of water and slowly added to 4,800 g of an aqueous solution of 3.5 % by weight of hydrochloric acid with stirring. After the addition, stirring was continued for five minutes, and a precipitated product was filtrated off. The obtained polymer was further added to 2 kg of HCFC-141b, followed by stirring for five minutes and filtrating off again. After that, the steps of washing with HCFC-141b and filtrating off were repeated four times, followed by vacuum drying at 120°C for 48 hours to give 140 g of polymer.
• a 500-ml four-necked flask equipped with a stirrer, thermometer and reflux tube was charged with 130 g of the polymer prepared in (1) above, 200 ml of methanol and 2 ml of sulfuric acid, and after 15-hour refluxing, was cooled to room temperature. After filtration of the reaction solution, 30 ml of methanol was added and washing by shaking was carried out for 10 minutes. After the washing by shaking with methanol three times, vacuum drying was carried out at 100°C for 3 hours to give 130 g of a polymer having, at the end, ester group obtained by methyl-esterification of carboxyl group. A conversion of the esterification to the polymer having ester group at the end was 95.6 % which was calculated from IR absorbance ratio of carbonyl group (1,769 cm -1 ) in carboxyl group before and after the reaction.
• TFE tetrafluoroethylene
• PMVE perfluoro(methyl vinyl ether)
• 1,000 Grams of the obtained aqueous dispersion was diluted with 3,000 g of water, followed by slowly adding to 2,800 g of an aqueous solution of 3.5 % by weight of hydrochloric acid with stirring. After the addition, stirring was continued for five minutes, and a precipitated product was filtrated off.
• the obtained polymer was further added to 800 g of HCFC-141b, followed by stirring for five minutes and filtrating off again. After that, the steps of washing with HCFC-141b and filtrating off were repeated four times, followed by vacuum drying at 120°C for 72 hours to give 72 g of a polymer having carboxyl group at the end and side chain.
• a 500-ml four-necked flask equipped with a stirrer, thermometer and reflux tube was charged with 130 g of the polymer prepared in (1) above, 200 ml of methanol and 2 ml of sulfuric acid, and after 15-hour refluxing, was cooled to room temperature. After filtration of the reaction solution, 30 ml of methanol was added and washing by shaking was carried out for 10 minutes. After the washing by shaking with methanol three times, vacuum drying was carried out at 100°C for 3 hours to give 130 g of a polymer having, at the end and side chain, ester group obtained by methyl-esterification of caboxyl group. A conversion of the esterification to the polymer having ester group at the end and side chain was 95.8 % which was calculated from IR absorbance ratio of carbonyl group in carboxyl group before and after the reaction.
• a dried 25-ml stainless steel bomb was charged with 0.83 g of perfluorooctanoic acid amide (available from PCR Inc.) and 1 ml of diethylene glycol dimethyl ether, and after pressure reduction to 5 mmHg, the bomb was sealed. Subsequently the inside pressure of the bomb was increased to 1.0 MPaG with COF 2 and the reaction was continued at room temperature. 24 Hours after, a remaining gas was exhausted and a reaction mixture was neutralized with 10 % aqueous solution of NaHCO 3 to a neutral level to separate into two phases. From the lower phase, 0.71 g of yellow oily substance was obtained. According to gas chromatography and GC mass spectrum analysis (column: SE-30), production of C 7 F 15 CN was recognized. A purity of the crude product was 89.5 % and a yield of the reaction was 80.1 %.
• a solid fluoroelastomer having, at the end, nitrile group functioning as a cure site and an economical preparation process thereof can be provided.
• Crosslinked products obtained from such a fluoroelastomer are excellent particularly in heat resistance, solvent resistance, chemical resistance, compression set, cleanliness, and the like, and can exhibit very excellent characteristics as various materials for sealing members, gaskets, hoses and rolls in the fields of semi-conductor production apparatuses, transportation means such as car, aircraft, rocket and vessel, chemical industries such as chemical plant and medical instruments and machinery such as developing machine, printing machine and coating facilities.

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